The present invention relates to a lens displacement mechanism using shaped memory alloy (SMA), especially to a lens displacement mechanism that uses SMA to control forward/backward movement of the lens for zooming and such mechanism is applied to an auto-focusing lens module.
Portable electronic devices such as digital cameras, mobile phones with camera function, or notebooks available now are generally disposed with auto-focusing (AF) compact camera, so called with auto-focusing lens module inside. The auto-focusing lens module primarily consists of a housing, a lens and a lens displacement mechanism. The lens is consists of a lens holder and a lens group. The lens holder and the lens group are mounted in the housing. The lens displacement mechanism is used for driving the lens in moving along an optical axis or toward/away from an object side by sliding or screw rotation for auto-focus control. A conventional lens displacement mechanism is composed of a piezoelectric motor that is formed by piezoelectric material. However, the general piezoelectric material is unable to endure high temperature of a reflow process. Once a special piezoelectric material that is durable to high temperature is used, the cost is quite expensive. As to another component, a voice coil motor (VCM), it uses magnetic force and includes elastic parts. But, under high temperature of the reflow process, the voice coil motor may be damaged or the magnetic force is reduced. Thus the reflow process is not used while assembling the piezoelectric motor or the voice coil motor. Therefore, this leads to difficulty in mass production. Furthermore, a SMA device formed by shaped memory alloy is used. By its principle of heat contraction and cold expansion, the lens is driven to move. The contraction and expansion amount of the SMA device is about 5%, far more effective than that of general material. Moreover, SMA device is durable to high temperature of the reflow process so that the reflow process can be applied when assembling the auto-focusing lens module. Therefore, the SMA device is practical and the assembling efficiency is improved.
Referring to patents of U.S. Pat. No. 5,185,621, U.S. Pat. No. 5,279,123, U.S. Pat. No. 5,459,544, U.S. Pat. No. 6,307,678, U.S. Pat. No. 6,449,434, US2002/0136548, US2007/0058070, US2007/0047938; WO2005/001540; Japan patents JP64-000938, JP09-127398, JP62-067738, JP03-196781, JP2006-329111, JP2005-275270, JP2005-195998, JP2005-156892, JP2004-184775, JP2004-129950, JP2004-069986, JP2004-038058, JP2000-056208; Taiwan patents TWM242178, TW200710464 and so on, all are prior arts relative to SMA devices in lens displacement mechanisms. Although they all use SMA devices as driving sources of lens displacement, the technique or driving way disclosed are different from one another. However, most of them have complicated design and large volume so that they can't match requirement of compact design of the lens modules. Referring to U.S. Pat. No. 6,449,434, a SMA wire is used. The two ends of the SMA wire is fixed and an intermediate moveable portion is hooked on a pivoted actuator. A projective pin is arranged on the outer edge of the actuator for locking with a slot on an outer edge of the lens holder as a stress point. By heating contraction and cold expansion of the SMA wire, the actuator is driven to pivot at an angle. Synchronously, the projective pin is also pivoted so as to drive the lens holder pivot at an angle. Thus by other element, the lens holder moves so as to achieve focusing. It is found that driving force is from the SMA wire, these prior arts still require some other linkage devices such as actuators, triggers or other leverage with similar functions to drive the lens holder in moving. The linkage device is disposed between the SMA wire and the lens holder so that contraction force of the SMA is converted into driving force for movement of the lens holder through the linkage device. Thus the movement and structure of the lens displacement mechanism are too complicated and this leads to negative effects on design requirements of compact lens module and low cost as well as has disadvantageous in mass production by SMT (Surface-Mount Technology). Therefore, there is still a space for improvement.